Method for making cathode active material of lithium ion battery

ABSTRACT

A method for making a cathode active material of a lithium ion battery is disclosed. In the method, LiMPO 4  particles and LiNPO 4  particles are provided. The LiMPO 4  particles and LiNPO 4  particles both are olivine type crystals belonged to a pnma space group of an orthorhombic crystal system, wherein M represents Fe, Mn, Co, or Ni, N represents a metal element having a +2 valence, and N is different from M. The LiMPO 4  particles and the LiNPO 4  particles are mixed together to form a precursor. The precursor is calcined to form LiM x N 1-x PO 4  particles, wherein 0&lt;x&lt;1.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims all benefits accruing under 35 U.S.C. § 119 fromChina Patent Application No. 201410066488.8, filed on Feb. 26, 2014 inthe China Intellectual Property Office, the content of which is herebyincorporated by reference. This application is a continuation under 35U.S.C. § 120 of international patent application PCT/CN2015/071319 filedJan. 22, 2015.

FIELD

The present disclosure relates to methods for making cathode activematerials of lithium ion batteries, and particular relates to a methodfor making a doped transition metal phosphate LiM_(x)N_(1-x)PO₄ as thecathode active material.

BACKGROUND

Olivine structure lithium metal phosphates LiMPO₄ are cathode activematerials in lithium ion batteries, with advantages including low-cost,environmental friendliness, high abundance, stable chemical properties,and excellent safety. One lithium metal phosphate is lithium ironphosphate (LiFePO₄), which has a theoretical capacity of 170 mAh/g andsuperior cycling capability. However, LiFePO₄ has a voltage plateau of3.4 V, which is a severe restriction of energy density of the lithiumion battery. LiMnPO₄, LiCoPO₄, and LiNiPO₄ have better energy density,but have relatively low electronic conductivities and lithium iondiffusion rates restricting the applications thereof. A solution forthis problem is doping the lithium metal phosphates to formLiM_(x)N_(1-x)PO₄ (e.g., LiMn_(x)Fe_(1-x)PO₄ or LiMn_(x)Mg_(1-x)PO₄).

Solvothermal synthesis and solid phase synthesis are two methods forsynthesizing the doped lithium metal phosphates LiM_(x)N_(1-x)PO₄. Thesolvothermal synthesis includes dissolving reactants in an organicsolvent and solvothermal heating the solution in an autoclave to obtainthe doped lithium metal phosphate. The solid phase synthesis includesball milling a mixture of the reactants with a solvent, and calciningthe milled mixture in an inert gas at a relatively high temperature toobtain the doped lithium metal phosphate.

BRIEF DESCRIPTION OF THE DRAWINGS

Implementations are described by way of example only with reference tothe attached figures.

FIG. 1 is a flow chart of an embodiment of a method for making a cathodeactive material of a lithium ion battery.

FIG. 2 shows X-ray diffraction (XRD) patterns of a precursor andLiMn_(0.4)Fe_(0.6)PO₄ particles in Example 1 before and after acalcining step.

FIG. 3 is a scanning electron microscope (SEM) image of theLiMn_(0.4)Fe_(0.6)PO₄ particles in Example 1.

FIG. 4A to FIG. 4D illustrate one embodiment of LiMnPO₄ particles,wherein FIG. 4A and FIG. 4B are SEM images at different resolutions,FIG. 4C is a transmission electron microscope (TEM) image, and FIG. 4Dis a Fourier transform (FT) image of the TEM image.

FIG. 4E to FIG. 4H illustrate one embodiment of LiMn_(0.4)Fe_(0.6)PO₄/Cparticles, wherein FIG. 4E and FIG. 4F are SEM images at differentresolutions, FIG. 4G is a TEM image, and FIG. 4H is a FT image of theTEM image.

FIG. 4I to FIG. 4L illustrate one embodiment of LiFePO₄ particles,wherein FIG. 4I and FIG. 4J are SEM images at different resolutions,FIG. 4K is a TEM image, and FIG. 4L is a FT image of the TEM image.

FIG. 5 shows XRD patterns of LiMn_(x)Fe_(1-x)PO₄/C particles in Example1 (x=0), Example 2 (x=2), Example 3 (x=4), Example 4 (x=6), Example 5(x=8), and Comparative Example 2 (x=1).

FIG. 6 shows element distributions of Fe and Mn inLiMn_(0.4)Fe_(0.6)PO₄/C particles in Example 3.

FIG. 7 is a graph showing discharge specific capacities at differentcurrent densities of LiMn_(x)Fe_(1-x)PO₄/C particles in Example 1 (x=0),Example 2 (x=2), Example 3 (x=4), Example 4 (x=6), Example 5 (x=8), andComparative Example 2 (x=1) as the cathode active materials.

FIG. 8 is graph showing energy densities at different current densitiesof LiMn_(x)Fe_(1-x)PO₄/C particles in Example 1 (x=0), Example 2 (x=2),Example 3 (x=4), Example 4 (x=6), Example 5 (x=8), and ComparativeExample 2 (x=1) as the cathode active materials.

DETAILED DESCRIPTION

It will be appreciated that for simplicity and clarity of illustration,where appropriate, reference numerals have been repeated among thedifferent figures to indicate corresponding or analogous elements. Inaddition, numerous specific details are set forth in order to provide athorough understanding of the embodiments described herein. However, itwill be understood by those of ordinary skill in the art that theembodiments described herein can be practiced without these specificdetails. In other instances, methods, procedures, and components havenot been described in detail so as not to obscure the related relevantfeature being described. Also, the description is not to be consideredas limiting the scope of the embodiments described herein. The drawingsare not necessarily to scale and the proportions of certain parts may beexaggerated to better illustrate details and features of the presentdisclosure.

Referring to FIG. 1, one embodiment of a method for making a cathodeactive material of a lithium ion battery comprises steps of:

S1, providing LiMPO₄ particles and LiNPO₄ particles both being olivinetype crystals belonging to a pnma space group of an orthorhombic crystalsystem, wherein M represents Fe, Mn, Co, or Ni, N represents a metalelement having a +2 valence, and N is different from M;

S2, mixing the LiMPO₄ particles and the LiNPO₄ particles together toform a precursor; and

S3, calcining the precursor to form LiM_(x)N_(1-x)PO₄ particles, wherein0<x<1.

In step S1, the LiMPO₄ particles and the LiNPO₄ particles have the samecrystal structure, which is an olivine type crystal structure belongingto a pnma space group of an orthorhombic crystal system. In oneembodiment, N can be one of Fe, Mn, Co, Ni, Mg, Ca, Zn, Cu, Al, B, Cr,Nb, Sc, Ti, V, Be, Sr, Ba, Zr, and La.

A shape of the LiMPO₄ particles and the LiNPO₄ particles can be at leastone of spheres, rods, and sheets. In one embodiment, the LiMPO₄particles and the LiNPO₄ particles are sheet shaped with which arelatively large contact surface area that is convenient for diffusionof the elements M and N during the calcining in step S4 can be formedbetween the particles. The LiMPO₄ particles and the LiNPO₄ particles canbe nanosized, have a relatively high reacting activity, and can be moreadaptable to promote a solid phase reaction during the calcining. In oneembodiment, both the LiMPO₄ particles and the LiNPO₄ particles arenanosheets.

The LiMPO₄ particles and the LiNPO₄ particles can have the same ordifferent morphologies. When the LiMPO₄ particles and the LiNPO₄particles have the same morphology, they can have the same or differentsizes. When both the LiMPO₄ particles and the LiNPO₄ particles arecrystals with the same crystal structure, the only difference betweenthe LiMPO₄ particles and the LiNPO₄ particles may be the difference inamount per unit volume (i.e., the molar concentration) of Fe and Mn.Therefore, during the calcining in step S4, only diffusion may occurbetween elements M and N in the LiMPO₄ particles and the LiNPO₄particles, and the morphology, crystal structure, and size of the LiMPO₄particles and the LiNPO₄ particles are maintained without change. Afterthe calcining in step S4, the LiMPO₄ particles may lose some of theelement M and gain some of the element N to form the LiM_(x)N_(1-x)PO₄particles. The LiM_(x)N_(1-x)PO₄ particles may inherit the morphology,crystal structure, and size of the LiMPO₄ particles. On the other hand,the LiNPO₄ particles may lose some of the element N and gain some of theelement M to form the LiM_(x)N_(1-x)PO₄ particles, and theLiM_(x)N_(1-x)PO₄ particles may inherit the morphology, crystalstructure, and size of the LiNPO₄ particles. Therefore, the morphologyand size of the LiM_(x)N_(1-x)PO₄ particles can be controlled bycontrolling the morphology and size of the LiMPO₄ particles and theLiNPO₄ particles. In one embodiment, the LiMPO₄ particles and the LiNPO₄particles have the same morphology and size to form theLiM_(x)N_(1-x)PO₄ particles having uniform morphology and size to obtaina more superior capability of the cathode active material.

In step S3, a ratio of the LiMPO₄ particles to the LiNPO₄ particles arenot limited and the value of x in the LiM_(x)N_(1-x)PO₄ particles can bedetermined by actual need. For example, if the value of x in theLiM_(x)N_(1-x)PO₄ particles is 4, a molar ratio of the LiMPO₄ particlesto the LiNPO₄ particles can be set to 4:6. Any ratio of the LiMPO₄particles to the LiNPO₄ particles can be used to obtain a high specificcapacity in the cathode active material if the element N is one of Fe,Mn, Co, and Ni. If N is one of Mg, Ca, Zn, Cu, Al, B, Cr, Nb, Sc, Ti, V,Be, Sr, Ba, Zr, and La, the ratio of the LiMPO₄ particles to the LiNPO₄particles can be set to have the value of x to be greater than 0.9 inthe LiM_(x)N_(1-x)PO₄ particles, which have a relatively high specificcapacity as the cathode active material.

The LiMPO₄ particles and the LiNPO₄ particles can be uniformly mixed toobtain the largest contact area therebetween in the precursor. Themixing is not limited except to avoid destroying the crystal structureand morphology of the LiMPO₄ particles and the LiNPO₄ particles. In oneembodiment, the LiMPO₄ particles and the LiNPO₄ particles are mixed in aliquid medium by ultrasonic agitation. In another embodiment, the LiMPO₄particles and the LiNPO₄ particles are nanosized which can be milledwithout destroying the crystal structure and the morphology.

Before the calcining step, the step S4 can further comprises a step ofadding a carbon source to the precursor. The carbon source and theprecursor are calcined together, during which the carbon source isdecomposed to coat an elemental carbon layer on the surfaces of theLiMPO₄ particles and the LiNPO₄ particles. After the calcining,LiM_(x)N_(1-x)PO₄/C particles can be obtained. The elemental carbonlayer can avoid an aggregation during the calcining between the LiMPO₄particles and the LiNPO₄ particles, to avoid an aggregation of theformed LiM_(x)N_(1-x)PO₄ particles. In addition, the electricalconductivity of the LiM_(x)N_(1-x)PO₄ particles can be improved.

The carbon source can be cracked into elemental carbon during thecalcining of step S4. The carbon source can be at least one of sucrose,glucose, Span 80, phenolic resin, epoxy resin, furan resin, polyacrylicacid, polyacrylonitrile, polyethylene glycol, and polyvinyl alcohol. Theamount of the carbon source can be decided according actual needs. Inone embodiment, the weight of the carbon source is 5% to 15% of a totalweight of the LiMPO₄ particles and the LiNPO₄ particles.

The carbon source can be added to the precursor by various ways if onlythe precursor and the carbon source are mixed together. For example, inone embodiment, the carbon source can be added during the mixing of theLiMPO₄ particles and the LiNPO₄ particles. In another embodiment, thecarbon source can be added to the precursor after the precursor isformed. In yet another embodiment, the precursor can be immersed in thecarbon source to mix with the carbon source. The carbon source, theLiMPO₄ particles, and the LiNPO₄ particles can be uniformly mixedtogether and then calcined to form the carbon layer uniformly coated onthe surfaces of the LiMPO₄ particles and the LiNPO₄ particles. In thepresent embodiment, the carbon source, the LiMPO₄ particles, and theLiNPO₄ particles are uniformly mixed with each other by a milling step.

In step S4, the calcining is processed at a temperature range from about300° C. to about 1200° C. In one embodiment, the temperature range canbe from about 500° C. to about 1000° C. The calcining can last for about2 hours to about 20 hours. In one embodiment, the calcining can last forabout 4 hours to about 10 hours. The calcining can be performed in aninert gas at a pressure of about 1 atm.

Example 1

0.016 mol of MnSO₄ and 0.048 mol of LiOH.H₂O are dissolved in 20 mL of amixed solvent of ethylene glycol and deionized water (a volume ratio ofthe ethylene glycol and the deionized water is about 4:1). 0.016 mol ofH₃PO₄ is added to this mixed solvent and mixed with the MnSO₄ and theLiOH to form a mixture. The mixture is solvothermal reacted at about180° C. for about 12 hours to form nanosheet shaped LiMnPO₄ particles.

0.016 mol of FeSO₄ and 0.048 mol of LiOH.H₂O are dissolved in 20 mL of amixed solvent of ethylene glycol and deionized water (a volume ratio ofthe ethylene glycol and the deionized water is about 4:1). 0.016 mol ofH₃PO₄ is added to this mixed solvent and mixed with the FeSO₄ and theLiOH to form a mixture. The mixture is solvothermal reacted at about180° C. for about 12 hours to form nanosheet shaped LiFePO₄ particles.

The nanosheet shaped LiMnPO₄ particles and the nanosheet shaped LiFePO₄particles are mixed in a molar ratio of 4:6 and the mixture is milledfor about 15 minutes to form the precursor. The precursor is calcined ina nitrogen gas environment at about 650° C. for about 5 hours to formLiMn_(0.4)Fe_(0.6)PO₄ particles.

Referring to FIG. 2, by comparing the XRD patterns of the precursorbefore the calcining and the LiMn_(0.4)Fe_(0.6)PO₄ particles formedafter the calcining, it can be seen that the diffraction peakscorresponding to LiMnPO₄ and LiFePO₄ disappear, and new diffractionpeaks appear at a position between the original LiMnPO₄ and LiFePO₄diffraction peaks. The new diffraction peaks have intensities that arestronger than the original LiMnPO₄ and LiFePO₄ diffraction peaks. Thenew diffraction peaks correspond to the LiMn_(0.4)Fe_(0.6)PO₄, whichmeans that the LiMnPO₄ particles and the LiFePO₄ particles completelyreact with each other and form pure, well crystallized, olivine typeLiMn_(0.4)Fe_(0.6)PO₄ particles. Referring to FIG. 3 and FIGS. 4A, 4B,4I, and 4J, the morphology of the LiMn_(0.4)Fe_(0.6)PO₄ particles, whichis the shape of nanosheet, is substantially the same with the morphologyof the LiMnPO₄ particles and the LiFePO₄ particles. In addition, thesize of the LiMn_(0.4)Fe_(0.6)PO₄ particles is also substantially thesame with the size of the LiMnPO₄ particles and the LiFePO₄ particles.

Example 2

0.016 mol of MnSO₄ and 0.048 mol of LiOH.H₂O are dissolved in 20 mL of amixed solvent of ethylene glycol and deionized water (a volume ratio ofthe ethylene glycol and the deionized water is about 4:1). 0.016 mol ofH₃PO₄ is added to this mixed solvent and mixed with the MnSO₄ and theLiOH to form a mixture. The mixture is solvothermal reacted at about180° C. for about 12 hours to form nanosheet shaped LiMnPO₄ particles.

0.016 mol of FeSO₄ and 0.048 mol of LiOH.H₂O are dissolved in 20 mL of amixed solvent of ethylene glycol and deionized water (a volume ratio ofthe ethylene glycol and the deionized water is about 4:1). 0.016 mol ofH₃PO₄ is added to this mixed solvent and mixed with the FeSO₄ and theLiOH to form a mixture. The mixture is solvothermal reacted at about180° C. for about 12 hours to form nanosheet shaped LiFePO₄ particles.

The nanosheet shaped LiMnPO₄ particles, the nanosheet shaped LiFePO₄particles, and sucrose are mixed and the mixture is milled for about 15minutes to form the precursor. A molar ratio of the LiMnPO₄ particles tothe LiFePO₄ particles is 2:8. A weight of sucrose is about 15% of atotal weight of the LiMnPO₄ particles and the LiFePO₄ particles. Theprecursor is calcined in nitrogen gas environment at about 650° C. forabout 5 hours to form LiMn_(0.2)Fe_(0.8)PO₄/C particles.

The lithium ion battery is assembled by using theLiMn_(0.2)Fe_(0.8)PO₄/C particles as the cathode active material. Thecathode comprises 80 wt % of LiMn_(0.4)Fe_(0.6)PO₄/C particles, 5 wt %of acetylene black, 5 wt % of conductive graphite, and 10 wt % ofpolyvinylidene fluoride. The anode is lithium metal. The separator is aCelgard 2400 polypropylene porous film. The electrolyte solution is 1mol/L of LiPF₆ dissolved in a mixed solvent of ethylene carbonate (EC),Diethyl carbonate (DEC), and ethylmethyl carbonate (EMC) (3:1:1, v/v/v).The CR2032 button type lithium ion battery is assembled in an argon gasfilled glove box, and rested in room temperature for a period of timebefore the electrochemical tests.

Example 3

Example 3 is substantially the same as Example 2, except that the molarratio of the LiMnPO₄ particles to the LiFePO₄ particles is 4:6, and theLiMn_(0.4)Fe_(0.6)PO₄/C particles are formed.

Comparative Example 1

Comparative Example 1 is substantially the same as Example 2, exceptthat the LiMn_(0.2)Fe_(0.8)PO₄ particles are replaced by nanosheetshaped LiFePO₄ particles, and the LiFePO₄/C particles are formed.

Comparative Example 2

Comparative Example 2 is substantially the same as Example 2, exceptthat the LiMn_(0.2)Fe_(0.8)PO₄ particles are replaced by nanosheetshaped LiMnPO₄ particles, and the LiMnPO₄/C particles are formed.

Referring to FIG. 5, the LiMnPO₄ and LiFePO₄ diffraction peaksdisappear, and new diffraction peaks corresponding toLiMn_(0.4)Fe_(0.6)PO₄ appear at a position between the original LiMnPO₄and LiFePO₄ diffraction peaks, which means that in Example 3, theLiMnPO₄ particles and the LiFePO₄ particles completely react with eachother and form the well crystallized LiMn_(0.4)Fe_(0.6)PO₄ particles.Referring to FIG. 4A to FIG. 4L, the morphology and size of theLiMn_(0.4)Fe_(0.6)PO₄/C particles is substantially the same with themorphologies and sizes of the LiMnPO₄ particles and the LiFePO₄particles. In addition, the LiMn_(0.4)Fe_(0.6)PO₄/C particles, theLiMnPO₄ particles, and the LiFePO₄ particles have the same growthdirection, which is along a bc plane of the crystal structure. There isno aggregation appeared in the LiMn_(0.4)Fe_(0.6)PO₄/C particles.Referring to FIG. 6, the distribution of element Fe is in accord withthe distribution of element Mn in the LiMn_(0.4)Fe_(0.6)PO₄/C particles,which means that a thorough solid phase reaction occurs. Inductivelycoupled plasma atomic emission spectroscopy (ICP-AES) is applied to theLiMn_(0.4)Fe_(0.6)PO₄/C particles, which reveals that a molar ratio ofMn to Fe in the LiMn_(0.4)Fe_(0.6)PO₄/C particles is 4:5.983, which hasa deviation smaller than 1% from the target stoichiometry. Therefore,the present method for making the LiMn_(0.4)Fe_(0.6)PO₄/C particles canprecisely control the stoichiometry of the reaction.

Example 4

Example 4 is substantially the same as Example 2, except that a molarratio of the molar ratio of the LiMnPO₄ particles to the LiFePO₄particles is 6:4, and the LiMn_(0.6)Fe_(0.4)PO₄/C particles are formed.

Example 5

Example 5 is substantially the same as Example 2, except that a molarratio of the LiMnPO₄ particles to the LiFePO₄ particles is 8:2, and theLiMn_(0.8)Fe_(0.2)PO₄/C particles are formed.

Referring to FIG. 7 and FIG. 8, compared to the LiFePO₄/C particles inComparative Example 1 and LiMnPO₄/C particles in Comparative Example 2,the LiMn_(x)Fe_(1-x)PO₄/C particles (x=0.2, 0.4, 0.6, and 0.8) inExamples 2 to 5 have superior cycling performances, rate capabilities,capacity retentions, and energy densities. Particularly, at a currentrate of 0.1 C, a discharge specific capacity of theLiMn_(0.4)Fe_(0.6)PO₄/C particles in Example 3 is about 160.6 mAh/g, andis 60% larger than the discharge specific capacity of the LiMnPO₄/Cparticles. After times of cycling, the LiMn_(0.4)Fe_(0.6)PO₄/C particlescan still maintain a relatively high capacity. An energy density of theLiMn_(0.4)Fe_(0.6)PO₄/C particles is 53% greater than the energy densityof the LiFePO₄/C particles. Therefore, the LiMn_(0.4)Fe_(0.6)PO₄/Cparticles not only have a relatively high specific capacity but alsohave a relatively high energy density.

The present method can overcome problems existed in the conventionalsolid phase synthesis and the conventional solvothermal synthesis. Theconventional solvothermal synthesis provides a complicated condition forthe reaction, and different metal ions have their own crystallizationbehaviors. Therefore, by using the conventional solvothermal synthesis,the stoichiometry of the product is uncontrollable. The conventionalsolid phase synthesis adopts powders of ammonium dihydrogen phosphate asthe phosphate source, lithium carbonate or lithium hydroxide as thelithium source, and ferrous oxalate/manganese (II) oxalate, ferrousacetate/manganese (II) acetate or manganese (II) carbonate as theiron/manganese source. During the high temperature calcining, elementsLi, P, and O in the reactants are diffused and recrystallized, whichgenerates defects in the crystal structure, and renders difficulty inmorphology and particle size controlling, for the reason that therecrystallization is greatly affected by the temperature, interfacialproperties, and crystal defects of the reactants.

The present method adopts the LiMPO₄ particles and the LiNPO₄ particleswith the same crystal structure as the precursor to have a precisecontrolling of the stoichiometry in a solid phase reaction. For thereason that there is only a concentration difference of the M and Nelements between the LiMPO₄ particles and the LiNPO₄ particles, duringthe calcining there is only a diffusion that occurs between elements Mand N in the LiMPO₄ particles and the LiNPO₄ particles, and themorphology, crystal structure, and size of the formed LiM_(x)N_(1-x)PO₄particles are inherited from the original LiMPO₄ particles and LiNPO₄particles. Accordingly, the morphology and size of the LiM_(x)N_(1-x)PO₄particles are capable of being controlled by controlling the morphologyand size of the LiMPO₄ particles and the LiNPO₄ particles. TheLiM_(x)N_(1-x)PO₄ particles formed by the present method as the cathodeactive material show superior cycling performances, rate capabilities,capacity retentions, and energy densities.

Depending on the embodiment, certain of the steps of methods describedmay be removed, others may be added, and the sequence of steps may bealtered. It is also to be understood that the description and the claimsdrawn to a method may comprise some indication in reference to certainsteps. However, the indication used is only to be viewed foridentification purposes and not as a suggestion as to an order for thesteps.

The embodiments shown and described above are only examples. Even thoughnumerous characteristics and advantages of the present technology havebeen set forth in the foregoing description, together with details ofthe structure and function of the present disclosure, the disclosure isillustrative only, and changes may be made in the detail, especially inmatters of shape, size, and arrangement of the parts within theprinciples of the present disclosure, up to and including the fullextent established by the broad general meaning of the terms used in theclaims. It will therefore be appreciated that the embodiments describedabove may be modified within the scope of the claims.

What is claimed is:
 1. A method for making a cathode active material ofa lithium ion battery, the method comprising: providing LiMPO₄ particlesand LiNPO₄ particles both being olivine type crystals belonging to apnma space group of an orthorhombic crystal system, wherein M representsFe, Mn, Co, or Ni, N represents a metal element having a +2 valence, andN is different from M; mixing the LiMPO₄ particles and the LiNPO₄particles together to form a precursor; and calcining the precursor toform LiM_(x)N_(1-x)PO₄ particles, wherein 0<x<1.
 2. The method of claim1, wherein both the LiMPO₄ particles and the LiNPO₄ particles arenanosized particles.
 3. The method of claim 1, wherein shapes of theLiMPO₄ particles and the LiNPO₄ particles are at least one of spheres,rods, and sheets.
 4. The method of claim 1, wherein both the LiMPO₄particles and the LiNPO₄ particles are sheet shaped.
 5. The method ofclaim 1, wherein both the LiMPO₄ particles and the LiNPO₄ particles arenanosheets.
 6. The method of claim 1, wherein the LiMPO₄ particles andthe LiNPO₄ particles have a same morphology and a same size.
 7. Themethod of claim 1, wherein both the LiMPO₄ particles and the LiNPO₄particles are nanosheets with a same size.
 8. The method of claim 1,wherein N is selected from the group consisting of Fe, Mn, Co, Ni, Mg,Ca, Zn, Cu, Al, B, Cr, Nb, Sc, Ti, V, Be, Sr, Ba, Zr, and La.
 9. Themethod of claim 1, wherein N is selected from the group consisting ofMg, Ca, Zn, Cu, Al, B, Cr, Nb, Sc, Ti, V, Be, Sr, Ba, Zr, and La, and aratio of the LiMPO₄ particles to the LiNPO₄ particles is set to havex>0.9.
 10. The method of claim 1, wherein the LiMPO₄ particles and theLiNPO₄ particles are uniformly mixed to form the precursor.
 11. Themethod of claim 1 further comprising a step of adding a carbon sourceinto the precursor before calcining the precursor to formLiM_(x)N_(1-x)PO₄ particles.
 12. The method of claim 1, wherein a weightof the carbon source is 5% to 15% of a total weight of the LiMPO₄particles and the LiNPO₄ particles.
 13. The method of claim 1, whereinthe carbon source is selected from the group consisting of sucrose,glucose, Span 80, phenolic resin, epoxy resin, furan resin, polyacrylicacid, polyacrylonitrile, polyethylene glycol, polyvinyl alcohol, andcombinations thereof.
 14. The method of claim 1, wherein the calciningoccurs at a temperature range from about 300° C. to about 1200° C. 15.The method of claim 14, wherein the temperature range is from about 500°C. to about 1000° C.
 16. The method of claim 1, wherein the calcining isprocessed in an inert gas.